Performance evaluation of an ALMA 12-m prototype antenna with an optical pointing telescope system

Details Performance evaluation of an ALMA 12-m prototype antenna with an optical pointing telescope system Performance evaluation of an ALMA 12-m prototype antenna with an optical pointing telescope system

Oct 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005rnaoj...8..111i&link_type=abstract

Report of the National Astronomical Observatory of Japan (ISSN 0915-6321), Vol. 8, No. 3 - 4, p. 111 - 123 (2005)

Computer Science

Performance

1

Radio Telescopes

Scientific paper

The optical pointing telescope (OPT) of 10-cm has been built to make performance evaluations of a proto-type 12-m radio telescope for the Atacama Compact Array project under actual operating conditions. The OPT system consists of an objective lens with a 2X extender, a peltier cooled CCD video camera, and an image acquisition & control computer. The plate scales were found to be 1.16 arcsec pixel-1. A red filter (R64) enabled us to make daytime observations of stars brighter than mv < 3.5 magnitude with a typical S/N larger than 20 by image integration of 1-3 seconds, which results in an error smaller than 0.1 arcsecond. The antenna testing was done at the VLA site of the National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico, US, where star image centroid motions sampled at 30 Hz at zenith were found to be typically 1.0 arcsec rms in March 2004. These results suggest that individual measurements with integration time of a few seconds give an error of star position determinations of 0.4-0.6 arcseconds rms. The whole sky absolute pointing error under no wind and during night was measured to be 1.17 arcseconds rms. We have applied retrospective thermal corrections to tracking data of several stars for two hours, with a preliminary thermal deformation model of the yoke, and have found the tracking accuracy improved to be 0.1-0.3 arcseconds rms for a 15-minute period. The OPT was also successfully used to demonstrate fast switching motion capability of the antenna that enables it to move back and forth between two positions of 1.5 degrees apart within 1.5 seconds and settle to within 3 arcsecond pointing error. A careful data analysis has revealed, however, that the antenna mount during the fast switching motion displays dumped oscillation at the dumped natural frequency of about 5 Hz with a decay time of about 1 second.

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